1. Field of the Invention
The present invention relates to a process for a diazo color formation reaction and a recording material utilizing the same, and more particularly, it relates to a process for an azo coupling reaction having a large reaction rate to realize quick color formation, and a recording material having a large color formation rate utilizing the reaction.
2. Description of the Related Art
Many reports have been made with respect to a reaction using a coupler and a diazonium salt and a recording material utilizing the color formation reaction. However, there are very few examples that use a coupler having a releasing group at the coupling site.
For example, J. Chem. Soc., Perkin Trans., 2 (1982) discloses a coupling reaction of an indole coupler having a releasing group at the coupling site and a p-nitrobenzene diazonium salt. However, the coupler having a releasing group introduced exhibits a remarkably low coupling rate in comparison to a non-substituted compound.
JP-A-6-297857 discloses an azo coupling reaction of a naphthol coupler having a dimethylaminomethyl group at the coupling site and a benzene diazonium salt. However, the color formation reaction has a problem in that a sufficient dye density cannot be obtained.
In addition to these report, it has been the general recognition that in the diazo color formation reaction system, introduction of a releasing group at the coupling site lowers the coupling activity.
Furthermore, a coupler having a releasing group has been widely studied and reported in many articles with respect to a coupler for photographic purposes using silver halide (for example, as described in Kaitei Shashin Kougaku no Kiso, Gin""en Shashin hen (Basis of Photographic Engineering, Revised Edition, Volume for Silver Halide Photograph), published by Corona Publishing Co., Ltd.
However, the releasing groups in the reports relating to a recording material using silver halide are defined as groups that can be released through reaction with an oxidized product of a coloring developing agent, such as quinone diimine. However, there have been no reports describing a compound having a group that can be released through reaction with a diazonium salt.
In the color formation reaction using a reaction of a coupler and a diazonium salt, the color formation reaction rate (i.e., the coupling rate) is one of the important characteristic features. For example, in a heat-sensitive recording material using a diazonium salt, a certain degree of speed of the reaction rate in azo coupling is demanded from the standpoint of practical recording rate. In general, the coupling rate is roughly defined by the skeleton of the coupler as assuming that the same diazonium salt is used. Therefore, the coupling rate can be increased by appropriately changing the species of the substituents on the positions other than the coupling site, but the stability of the coupler is then lowered to cause various problems. For example, a heat-sensitive recording material suffers a problem in that the exposure coloring on the background part of a coupler having a good reaction rate tends to be increased.
Consequently, the coupling activity and the stability of the coupler tend to counter each other. Therefore, such a method has not yet been found that is effective to greatly improve the coupling activity of a certain coupler skeleton without greatly impairing the stability of the coupler.
The present invention has been developed to solve the problems associated with the conventional techniques described in the foregoing and to attain the following object.
An object of the present invention is to provide a process for an azo coupling reaction with high coupling activity using a stable coupler having a large reaction rate and an excellent coloring density, and also is to provide a recording material containing the coupler excellent in stability and reaction rate by utilizing the process for azo coupling reaction.
The inventors have found that the object is attained by a process for a diazo color formation reaction using the following coupler having a releasing group and a recording material containing the coupler, and thus the invention has been completed.
The process for an azo coupling reaction of the present invention comprises carrying out a coupling reaction of a diazonium salt and a coupler to make the diazonium salt form color, the coupler having one of the structures represented by the following general formulae (1), (2) and (3): 
wherein X1, X2, X3 and X4 each independently represents an atomic group necessary for forming a 5-membered aromatic heterocyclic ring; Y represents an amino group, a substituted amino group, a hydroxyl group, an alkoxy group, an alkyl group, which may have a substituent, provided that X1 and Y may be combined to form a heterocyclic ring; L represents a substituent capable of being released as a carbonium ion upon coupling with the diazonium salt; and EWG1 and EWG2each independently represents an electron withdrawing group, provided that EWG1 and EWG2 may be combined to form a heterocyclic ring.
It is preferable that the substituent represented by L of the coupler is a substituent represented by the following general formula (4):
xe2x80x94CHR1R2
wherein at least one of R1 and R2 contains an electron sourse capable of stabilizing a carbonium ion by resonance, i.e., a heteroatom having an unpaired electron.
It is preferable that the 5-membered heterocyclic ring of the coupler having a structure represented by the general formula (1) or (2) is one of a pyrrole ring, a pyrazole ring and an imidazole ring.
It is preferable that EWG1 and EWG 2 of the coupler having a structure represented by the general formula (3) each is a carbonyl group.
It is preferable that the diazonium salt as the other component involving the azo coupling reaction of the invention is a benzene diazonium salt represented by the following general formula (5): 
wherein R3, R4 and R5, which may be the same or different, each independently represents an alkyl group, an aryl group, an aralkyl group, an alkenyl group, a heterocyclic group or an acyl group; Y1 represents an oxygen atom, a sulfur atom or an amino group; Y2 represents an oxygen atom or a sulfur atom; Y3 represents an oxygen atom, a sulfur atom or a hydrogen atom, provided that when Y3 represents a hydrogen atom, R5 is not present; and Xxe2x88x92represents an anion.
In the process for an azo coupling reaction of the present invention, it is preferable that a reaction rate of the reaction k is 0.1 (sxe2x88x921) or more. When the process for an azo coupling reaction of the present invention is employed, the color formation reaction of the diazonium salt and the coupler effectively proceeds owing to the excellent stability and the large reaction rate, and thus the coloring density of the diazonium salt used is sufficiently exerted. When the coloring rate is small, on the other hand, the probability of inactivation of the diazo compound with the lapse of time during the reaction increases, and thus sufficient coloring density is difficult to be obtained.
The recording material of the present invention comprises a coupler having one of the structures represented by the following general formulae (1), (2) and (3), and a diazonium salt capable of coloring through a coupling reaction with the coupler.
As preferable embodiments of the recording material, it is preferable that the diazonium salt is encapsulated in microcapsules, and it is more preferable from the standpoint of reactivity that an emulsion containing the coupler contains an organic base.
A process for an azo coupling reaction of the present invention using a diazonium salt and a coupler having a releasing group, and a recording material containing the coupler will be described below.
When a coupler that is coupled with a diazonium salt in an ordinary method for an azo coupling reaction is represented by the following general formula (6), the group that contributes to the reaction is xe2x80x94H. Upon applying the expression to the process for an azo coupling reaction of the present invention, the coupler having a releasing group can be represented by the following general formula (7):
Cpxe2x80x94Hxe2x80x83xe2x80x83(6)
Cpxe2x80x94Lxe2x80x83xe2x80x83(7)
wherein Cp represents a mother nucleus of the coupler; H represents a hydrogen atom; and L represents a substituent capable of being released as a carbonium ion upon coupling with the diazonium salt (hereinafter sometimes referred to as a xe2x80x9creleasing groupxe2x80x9d).
The xe2x80x9ccoupling ratexe2x80x9d referred to in the present invention is defined as a value that is obtained by the following measurement method in view of the constraint of the diazonium salt participating in the reaction.
An ethyl acetate solution containing the diazonium salt in 8xc3x9710xe2x88x925 M and an ethyl acetate solution containing the coupler and the base in 8xc3x9710xe2x88x923 M, respectively, are mixed in an equivalent ratio by using a stopped-flow measuring device (RA-401, produced by Otsuka Electronics Co., Ltd.). The change with the lapse of time of the absorbance of the dye thus formed is measured, and the coupling rate constant (k) is calculated from the following equation (1):
d[dye]/dt=k[diazonium salt]xe2x80x83xe2x80x83Equation (1)
In the equation (1), k represents the coupling rate constant (sxe2x88x921), t represents the time (s), [dye] represents the produced molar amount of the dye (mol), and [diazonium salt] represents the initial molar amount of the diazonium salt (mol).
The coupler used in the process for an azo coupling reaction of the present invention has one of the structures represented by the general formulae (1), (2) and (3), and L in the general formulae (1), (2) and (3) represents a substituent capable of being released as a carbonium ion upon coupling with the diazonium salt (releasing group). Only one of the releasing group L may be introduced into the mother nucleus of the coupler as a substituent, or two or more thereof may be introduced. 
The releasing group represented by L is preferably a substituent represented by the general formula (4):
xe2x80x94CHR1R2xe2x80x83xe2x80x83(4)
wherein at least one of R1 and R2 contains an electron source capable of stabilizing a carbonium ion by resonance, i.e., a heteroatom having an unpaired electron, such as an oxygen atom and a nitrogen atom.
Preferable examples of the group represented by R1 and R2include a hydroxyl group, an amino group, a mercapto group, an alkoxy group, an aryloxy group, a substituted amino group, a substituted mercapto group, and an aromatic group and an ethylene group substituted by these substituents.
In the case where R1 is the group having an electron source capable of stabilizing a carbonium ion by resonance, preferable examples of R2 include a hydrogen atom, an alkyl group and an aryl group.
In the case where two or more of the releasing groups L are introduced as substituents, they may be the same or different, and these substituents may further have the substituents described in the foregoing.
More specifically, in the case where R2 is a hydrogen atom, preferable examples of the releasing group L include a hydroxymethyl group, an aminomethyl group, a mercaptomethyl group, an alkoxymethyl group (such as a methoxymethyl group and an ethoxymethyl group), an aryloxymethyl group (such as a phenoxymethyl group and a p-toluyloxymethyl group), a substituted aminomethyl group (such as a dimethylaminomethyl group, a diarylaminomethyl group and a phenylmethylaminomethyl group), a substituted mercaptomethyl group (such as a thioethoxymethyl group and a thiophenoxymethyl group), a hydroxybenzyl group, an alkoxybenzyl group (such as a methoxybenzylmethyl group), an aminobenzyl group, a substituted aminomethyl group (such as dimethylaminobenzyl group and a diarylaminobenzyl group), a mercaptobenzyl group, a substituted mercaptobenzyl group (such as a thiomethoxybenzyl group and a thiophenoxybenzyl group) and a dimethylaminopropenyl group.
In the case where R1 is a group or an atom other than hydrogen, preferable examples of the releasing group L include a releasing group represented by the following structural formulae. 
In the case where R1 and R2 are substituents having an electron source capable of stabilizing a carbonium ion by resonance, preferable examples of the releasing group L include a bisethoxymethyl group, a bisdimethylaminomethyl group, a bisthiomethoxymethyl group and a releasing group represented by the following structural formulae. 
The 5-membered heterocyclic ring of the coupler having the structure represented by the general formula (1) or (2) is preferably one of a pyrrole ring, a pyrazole ring and an imidazole ring.
EWG1 and EWG2 of the coupler having the structure represented by the general formula (3) each independently represents an electron drawing group, provided that EWG1 and EWG2 may be combined to form a heterocyclic ring, and EWG1 and EWG2 each is preferably a carbonyl group.
Specific examples of compounds that are preferably used as the coupler in the present invention include the following compounds (C-1) to (C-33), but the present invention is not limited to these compounds. The compounds (C-1) to (C-18) are examples of the compound having the structure represented by the general formula (1), the compounds (C-19) to (C-26) are examples of the compound having the structure represented by the general formula (2), and the compounds (C-27) to (C-33) are examples of the compound having the structure represented by the general formula (3). 
The coupler compound having a releasing group that can be used in the invention can be synthesized by various methods, and in general, a corresponding coupler (having no substituent at the coupling site) is reacted with a suitable reagent. For example, a hydroxymethyl releasing group can be synthesized in such a manner that a formyl group is introduced by using a Vilsmeier reagent, and then the formyl group is reduced. A dimethylaminomethyl releasing group can be synthesized by reacting with a Mannich reagent. Various kinds of substituted hydroxymethyl groups can be synthesized by adding an aldehyde to the coupler.
The diazonium salt that colors through reaction with the coupler in the process for azo coupling reaction of the invention is not particularly limited, and a diazonium salt compound represented by the following general formula (A) can be used through arbitrary selection. The diazonium salt is a compound that is colored through a coupling reaction with the coupler under application of heat and is decomposed by light.
Arxe2x80x94N2+Xxe2x88x92xe2x80x83xe2x80x83(A)
wherein Ar represents an aromatic part, and Xxe2x88x92 represents an acid anion.
The diazonium salt is preferably a benzene diazonium salt represented by the general formula (5): 
wherein R3, R4 and R5, which may be the same or different, each independently represents an alkyl group, an aryl group, an aralkyl group, an alkenyl group, a heterocyclic group or an acyl group; Y1 represents an oxygen atom, a sulfur atom or an amino group;Y2 represents an oxygen atom or a sulfur atom; Y3 represents an oxygen atom, a sulfur atom or a hydrogen atom, provided that when Y3 represents a hydrogen atom, R5 is not present; and Xxe2x88x92 represents an anion.
Y1 preferably represents a sulfur atom or an amino group, and in the case where Y1 is an amino group, it may have a substituent. Examples of the substituent include an alkyl group, an aryl group and an aralkyl group. Y1 and R3 may form a ring. Examples of the ring include a pyrrolidinyl group, a piperidinyl group and a piperazinyl group, which may have a substituent.
It is more preferable that Y1 is a sulfur atom, and Y2 and Y3 are oxygen atoms.
In the case where R3, R4 and R5 are alkyl groups, an alkyl group having from 1 to 30 carbon atoms is preferable, which may be either linear, branched or cyclic and may have a substituent. Examples of the substituent include an alkoxy group, an aryloxy group, a halogen atom, an alkylamino group, an arylamino group, an amino group, a carbamoyl group, a hydroxyl group, an acyloxy group, an alkoxycarbonyl group and an acylamino group. The substituent may further have a substituent. Examples of the substituted or unsubstituted alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a sec-pentyl group, a methoxyethyl group, an ethoxyethyl group and an acetoxyethyl group.
In the case where R3, R4 and R5 are aryl groups, an aryl group having from 6 to 30 carbon atoms is preferable, examples of which include a phenyl group and a naphthyl group. The aryl group may have a substituent, and examples of the substituent include an alkoxy group, an aryloxy group, a halogen atom, an alkylamino group, an arylamino group, an amino group, a carbamoyl group, a hydroxyl group, an acyloxy group, an alkoxycarbonyl group and an acylamino group. The substituent may further have a substituent.
In the case where R3, R4 and R5 are aralkyl groups, an aralkyl group having from 7 to 30 carbon atoms is preferable, examples of which include a benzyl group and a phenethyl group. The aralkyl group may have a substituent, and examples of the substituent include an alkoxy group, an aryloxy group, a halogen atom, an alkylamino group, an arylamino group, an amino group, a carbamoyl group, a hydroxyl group, an acyloxy group, an alkoxycarbonyl group and an acylamino group.
In the case where R3, R4 and R5 are alkenyl groups, an alkenyl group having from 2 to 20 carbon atoms is preferable, examples of which include a 4-pentenyl group, a 5-hexenyl group, a 3-methyl-3-butenyl group and a crotyl group. The alkenyl group may have a substituent, and examples of the substituent include an aryl group, an alkoxy group, an aryloxy group, a halogen atom, an alkylamino group, an arylamino group, an amino group, a carbamoyl group, a hydroxyl group, an acyloxy group, an alkoxycarbonyl group and an acylamino group.
In the case where R3, R4 and R5 are heterocyclic groups, a heterocyclic group having nitrogen, oxygen and/or sulfur as a heteroatom is preferable, which may be either saturated, unsaturated, monocyclic or condensed ring, examples of which include furyl, thienyl, oxazolyl, thiazolyl, imidazolyl, pyrazolyl, pyridyl, pyrimidyl, piperidyl, piperidyno, morpholinyl, morpholino, piperazinyl, indolyl, isoindolyl and quinolyl. The heterocyclic group may have a substituent, and examples of the substituent include an alkyl group, an aryl group, an alkoxy group, an aryloxy group, a halogen atom, an alkylamino group, an arylamino group, an amino group, a hydroxyl group, an acyl group, an acyloxy group, an alkoxycarbonyl group and an acylamino group.
In the case where R3, R4 and R5 are acyl groups, an acyl group having from 2 to 20 carbon atoms is preferable, which may be either aliphatic, aromatic or heterocyclic, examples of which include an acetyl group, a propanoyl group, a butanoyl group, a hexanoyl group, a 2-ethylhexanoyl group and a benzoyl group. The acyl group may have a substituent, and examples of the substituent include an alkoxy group, an aryloxy group, a halogen atom, an alkylamino group, an arylamino group, an amino group, a hydroxyl group, an acyloxy group, an alkoxycarbonyl group and an acylamino group.
Among these, R3 is preferably a substituted aryl group having from 6 to 20 carbon atoms, and a 4-chlorophenyl group, a 2-N-substituted carbamoylphenyl group, a 4-N-substituted carbamoylphenyl group, a 3-tolyl group, a 4-tolyl group and a 2,5-dichlorophenyl group are more preferable.
R4 and R5 each is preferably an alkyl group having from 1 to 20 carbon atoms or an alkenyl group having from 3 to 20 carbon atoms.
Examples of the acid anion (Xxe2x88x92) include a perfluoroalkyl carboxylic acid having from 1 to 20 carbon atoms (such as perfluorooctanoic, perfluorodecanoic acid and perfluorododecanoic acid), a perfluoroalkylsulfonic acid having from 1 to 20 carbon atoms (such as perfluorooctanesulfonic acid, perfluorodecanesulfonic acid and perfluorohexadecanesulfonic acid), an aromatic carboxylic acid having from 7 to 50 carbon atoms (such as 4,4-di-t-butylsalicylic acid, 4-t-octyloxybenzoic acid, 2-n-octyloxybenzoic acid, 4-n-hexadecylbenzoic acid, 2,4-bis-n-octadecyloxybenzoic acid and 4-n-decylnaphthoic acid), an aromatic sulfonic acid having from 6 to 50 carbon atoms (such as 1,5-naphthalenedisulfonic acid, 4-t-octyloxybenzenesulfonic acid and 4-n-dodecylbenzenesulfonic acid), 4,5-di-t-butyl-2-naphthoic acid, tetrafluoroboric acid, tetraphenylboric acid and hexafluorophosphoric acid. Among these, a perfluoroalkylcarboxylic acid having from 6 to 16 carbon atoms, a perfluoroalkylsulfonic acid having from 6 to 16 carbon atoms, an aromatic carboxylic acid having from 10 to 40 carbon atoms, an aromatic sulfonic acid having from 10 to 40 carbon atoms, tetrafluoroboric acid, tetraphenylboric acid and hexafluorophosphoric acid are preferable.
The reason why these diazonium salts are preferably used is that these exert a large effect to increase the reaction rate owing to the introduction of the releasing group.
Specific examples of the diazonium salt used in the invention include the following compounds (D-1) to (D-39), but the present invention is not limited to these compounds. 
In the process for an azo coupling reaction of the present invention, the amount ratio of the coupler and the diazonium salt can be appropriately selected depending on the compounds used, and the coupler is preferably used in an amount of from 1.0 to 10.0 parts by mass, and more preferably from 1.0 to 2.0 parts by mass, per 1 part by mass of the diazonium salt. When it is less than 1.0 part by mass, sufficient color formation cannot be obtained, and when it exceeds 10.0 parts by mass, no further increase of the effect is obtained.
In the process for an azo coupling reaction of the present invention, a sufficient reaction rate is obtained by the coupler having a releasing group, and the effect is outstanding when the coupler represented by the general formulae (1) to (3) and the diazonium salt compound represented by the general formula (5) are used.
In the process for an azo coupling reaction of the present invention, an organic base may be used for accelerating the coupling reaction. Examples of the base used include a guanidine compound, a tertiary amine compound, a pyridine compound, a piperidine compound, an amidine compound, a formamidine compound and a morpholine compound. Among these, a guanidine compound and a tertiary amine compound are preferable. Furthermore, the organic bases described in JP-A-57-123086, JP-A-60-49991, JP-A-60-94381, JP-A-9-71048, JP-A-9-77729 and JP-A-9-77737 may also be used.
Specific examples of the organic base that is preferably used in the process for an azo coupling reaction of the present invention include the following compounds (B-1) to (B-8), but the present invention is not limited to these compounds. 
The amount of the organic base used is not particularly limited, and it is preferable to use in an amount of from 1 to 30 mol per 1 mol of the diazonium salt.
The recording material of the present invention utilizing the azo coupling reaction and having excellent stability and a high coloring rate will be described below.
The recording material of the present invention comprises a coupler having one of the structures represented by the general formulae (1), (2) and (3), and a diazonium salt capable of coloring through a coupling reaction with the coupler. 
wherein X1, X2, X3 and X4 each independently represents an atomic group necessary for forming a 5-membered aromatic heterocyclic ring; Y represents an amino group, a substituted amino group, a hydroxyl group, an alkoxy group, an alkyl group, which may have a substituent, provided that X1 and Y may be combined to form a heterocyclic ring; L represents a substituent capable of being released as a carbonium ion upon coupling with the diazonium salt; and EWG1 and EWG2each independently represents an electron withdrawing group, provided that EWG1 and EWG2 may be combined to form a heterocyclic ring.
The coupler and the diazonium salt contained in the recording material are the same as those described for the process for an azo coupling reaction, and preferable examples thereof are also the same.
The recording material of the present invention may be either a heat-sensitive recording material or a diazo photosensitive recording material as long as it utilizes an azo coupling reaction for color formation. Because it is particularly excellent in coloring rate and stability, the effect thereof is outstanding when it is applied to a heat-sensitive recording material capable of carrying out imagewise recording with a thermal head or laser.
A heat-sensitive recording material will be described below as an example of the recording material of the present invention.
The diazonium salt used in the recording material of the present invention is a compound that is colored through a coupling reaction with the coupler under application of heat and is decomposed by light. The maximum absorption wavelength thereof can be controlled by the position and the species of the substituent at the portion of Ar in the general formula (A).
The diazonium salt used in the recording material of the present invention preferably contains 12 or more carbon atoms and preferably has a solubility in water of 1% or less and a solubility in ethyl acetate of 5% or more.
The diazonium compound may be used singly or in combination of two or more kinds thereof in accordance with various purposes such as hue adjustment.
The diazonium salt is preferably used in a recording layer of the recording material in an amount of from 0.01 to 3 g/m2, and more preferably from 0.02 to 1.0 g/m2. When the amount is less than 0.01 g/m2, sufficient color formation cannot be obtained, and when it exceeds 3 g/m2, it is not preferable since the sensitivity is lowered, and the fixing time is necessarily prolonged.
In the case where the diazonium salt used in the recording material of the present invention is used in the heat-sensitive recording material, it is preferable that the diazonium salt is encapsulated in microcapsules to improve the storage stability before use.
The production of the microcapsules can be attained by the known processes.
Examples thereof include interface polymerization processes described in U.S. Pat. No. 3,287,154, British Patent No. 990,443, JP-B-38-19574, JP-B-42-446 and JP-B-42-771, a process using an isocyanate polyol wall material described in U.S. Pat. No. 3,914,511, a process using an isocyanate wall material described in U.S. Pat. No. 3,914,511, and an in situ process by polymerization of a monomer described in JP-B-36-9168 and JP-A-51-9079.
The process for encapsulating in microcapsules is not limited to these processes. In a photosensitive heat-sensitive transfer material, an interface polymerization process is particularly preferable. In this process, an oily phase is formed by dissolving or dispersing a coloring component in a hydrophobic organic solvent to be a core of the capsule, and an aqueous phase is formed by dissolving a water soluble polymer. The oily phase and the aqueous phase are mixed and dispersed for emulsification, for example, by a homogenizer, and then the mixture is heated to conduct a polymer formation reaction at the interface of oil droplets, so as to form a microcapsule wall composed of the polymer.
Consequently, capsules having a uniform particle diameter can be formed in a short period of time to produce a recording material excellent in storage stability before use. The process for forming microcapsules is described in detail, for example, in JP-A-2-141279.
The coupler compound forms a dye through coupling with the diazonium compound in a basic atmosphere and/or a neutral atmosphere, and can be used by combining plural kinds thereof for various purposes, such as hue adjustment.
The coupler compound can be added to the recording layer in an amount of from 0.02 to 5 g/m2, and is more preferably added in an amount of from 0.1 to 4 g/m2 from the standpoint of the effect. When the added amount is less than 0.02 g/m2, it is not preferable since the color formation is poor, and when it exceeds 5 g/m2, it is also not preferable since the coating property is deteriorated.
The coupler compound is used in combination with the diazonium salt.
In this case, the coupler compound is preferably used in an amount of from 0.5 to 20 parts by mass, and more preferably from 1 to 10 parts by mass, per 1 part by mass of the diazonium salt. When it is less than 0.5 part by mass, sufficient color formation cannot be obtained, and when it exceeds 20 parts by mass, it is not preferable since the coating property is deteriorated.
While the coupler compound can be used through solid dispersion, for example, by a sand mill, after adding a water soluble polymer along with other component, it is preferable that the coupler is emulsified with a suitable emulsification assistant to be used as an emulsion. The methods for solid dispersion and emulsification herein are not particularly limited, and those known in the conventional art can be employed. The methods are described in detail in JP-A-59-190886, JP-A-2-141279 and JP-A-7-17145.
In the recording material of the present invention, it is also preferable to use an organic base in combination as described for the process for azo coupling reaction. In the case where the base is used in combination, it is preferable that the organic base is added to the emulsion dispersion of the coupler and mixed.
The recording material of the present invention may comprise a known support having formed thereon a recording layer containing the coupler and the diazonium salt. As long as the effects of the present invention are not compromised, known additives used in recording materials may be used in combination, and other layers, such as an undercoating layer, a protective layer and an ultraviolet ray absorbing layer, may be provided in addition to the support and the recording layer.
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.